fix(storage): throw a SupabaseStorageException for a non-JSON 2xx body

packages/Storage/Storage.Tests/Files/StorageFileApiContractTests.cs

@@ -392,6 +392,22 @@ public async Task List_ShouldSurfaceStorageException_GivenNonJsonError()
         }
     }
 
+    [TestMethod]
+    public async Task List_ShouldSurfaceStorageException_GivenNonJsonSuccessBody()
+    {
+        const string body = "<html><body>502 Bad Gateway</body></html>";
+        this.server.Given(Request.Create().WithPath($"/storage/v1/object/list/{Bucket}").UsingPost())
+            .RespondWith(Response.Create().WithStatusCode(200).WithBody(body));
+        var act = () => this.client.From(Bucket).List();
+        var exception = (await act.Should().ThrowAsync<SupabaseStorageException>(
+            "storage-js reports a non-JSON 2xx body as a StorageUnknownError, not a raw parse error")).Which;
+        using (new AssertionScope())
+        {
+            exception.StatusCode.Should().Be(200);
+            exception.Content.Should().Be(body);
+        }
+    }
+
     [TestMethod]
     public async Task UploadToSignedUrl_ShouldForwardMetadataAndCustomHeaders_GivenFileOptions()
     {

packages/Storage/Storage/Helpers.cs

@@ -74,6 +74,21 @@ internal static HttpClient ResolveDownloadClient(ClientOptions options) =>
         var response = await MakeRequestAsync(httpClient, retry, method, url, data, headers, cancellationToken);
         var content = await response.Content.ReadAsStringAsync();
 
+        // A proxy can answer 2xx with an HTML page; JSON that doesn't fit T still throws below.
+        try
+        {
+            JsonDocument.Parse(content).Dispose();
+        }
+        catch (JsonException e)
+        {
+            throw new SupabaseStorageException(e.Message, e)
+            {
+                Content = content,
+                Response = response,
+                StatusCode = (int) response.StatusCode,
+            };
+        }
+
         return JsonSerializer.Deserialize<T>(content, SerializerOptions);
     }